var bar = {
  myName: "time.geekbang.com",
  printName: function () {
    console.log(this.myName)
  }
}

function foo() {
  let myName = "极客时间"
  return bar.printName
}

let myName = "极客邦"
let _printName = foo()
_printName()//undefined 因为this相当于是window
bar.printName()//time.geekbang.com 因为this是bar

